I have a fused disconnect as my service disconnect feeding a fire pump. In order to comply with the NEC requirement to NOT provide overload protection in the overcurrent device feeding the FP, should I be providing a non-time delay fuse (i.e. instantaneous only protection)?
Fire Pump Fuse Type
- Thread starter msteiner
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alive wire
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- Location
- Phoenix, AZ US
695.5(B) says secondary overcurrent protection shall not be permitted, I interpret that as no fusible disconnect
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alive wire
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- Phoenix, AZ US
Fire pumps are really kind of cool, one of the only circuits we get to build for a meltdown situation
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695.5(B) refers to transformer secondary, and applies when you have a transformer downstream of the utility service entrance. My fused disconnect is serving as the utility service disconnect.
alive wire
Member
- Location
- Phoenix, AZ US
Why does it have to be fused why can't it just be a disconnect ? Reading through article 695 right now
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alive wire
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- Phoenix, AZ US
I definitely don't know everything which is why I hang out on this forum, but if the goal of running a fire pump is to keep it going to catastrophic failure
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alive wire
Member
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- Phoenix, AZ US
Sorry premature send wouldn't you want to use a time delay fuse
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I guess my question really has to do with fuse trip characteristics. If I were using a circuit breaker I would call for a motor circuit protector type, with magnetic-only protection, and no overload protection. I don't know what fuse type is analogous to an MCP breaker.
mayanees
Senior Member
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- Westminster, MD
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- Electrical Engineer and Master Electrician
'sup Matt
'sup Matt
NFPA 20, section 9.2 "Normal Power" requires disconnect and overcurrent protection to occur in the listed fire pump controller, so I don't think a disconnect ahead of the controller is allowed.
Fusing in the controller is sized to allow locked rotor current indefinitely, and the type would be driven by the mounting arrangement in the controller and the required ampacity and voltage.
'sup Matt
NFPA 20, section 9.2 "Normal Power" requires disconnect and overcurrent protection to occur in the listed fire pump controller, so I don't think a disconnect ahead of the controller is allowed.
Fusing in the controller is sized to allow locked rotor current indefinitely, and the type would be driven by the mounting arrangement in the controller and the required ampacity and voltage.
gadfly56
Senior Member
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- New Jersey
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- Professional Engineer, Fire & Life Safety
If you use a fused disconnect, it should be sized for the locked rotor current. Same with anything that might be further upstream.
Tony S
Senior Member
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- Resting under the Major Oak UK
For security of supply to fire pumps this is one of the best setups I’ve come across. The two red switches are direct off the transformer incoming. Even if the main LV breaker trips the pump supply is assured (Incoming isolated in this picture). The board had two incomers and therefore four pumps in total.
The supply to the fire pump panels was MI.
The supply to the fire pump panels was MI.
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